In measuring a specific component in body fluid (e.g. glucose in blood), redox reaction is utilized in general. A handy-size blood measuring device is generally used for the easy measurement of blood sugar at or away from home. In use, a disposal biosensor for providing an enzyme reaction field is attached to this simple blood sugar measuring device. When supplied with blood, the biosensor measures blood sugar level in blood (see JP-B-H08-10208 for example).
The biosensors may be different in sensitivity. Such difference is often made by change in component materials or in design for production lines. Particularly on launching the production lines, optimization in production conditions and material selection may cause the biosensors to differ in sensitivity. Further, when the production of the biosensors is performed at a plurality of factories or one factory but on the plural production lines, the biosensors produced at the different factories or on the different lines may also differ in sensitivity. Therefore, the blood sugar measuring device is often provided in advance with a plurality of calibration curves to measure concentrations correctly with the biosensors varying in sensitivity. With the blood sugar measuring device capable of measuring a plurality of measurement items such as a blood sugar level and a cholesterol level, the plural calibration curves are needed for the measurement items. In these cases, the measuring device must recognize information about a calibration curve suitable for the sensitivity of the biosensor and the measurement items to select such a calibration curve.
As a first example method of determining the calibration curve, each calibration curve is assigned with an identification code in advance. The biosensor is also assigned with an identification code, which is displayed on a case of the biosensor or in a user instruction. In this example, the blood sugar measuring device is installed with a program for determining the calibration curve in advance. When a user operates a button in the blood sugar measuring device, the calibration curve is determined.
As a second example method for determining the calibration curve, the case accommodates the plural biosensors and a correction chip for outputting information about the calibration curve suited to the biosensor. In this example, when the correction chip is inserted into the blood sugar measuring device in the same manner as is the biosensor, the concentration measuring device determines the calibration curve automatically (see e.g. JP-A-H08-20412).
However, when the user determines the calibration curve by the button operation, the operation is a burden to the user. Further, he or she may forget to perform the operation. Similarly, the use of the correction chip is a burden to the user, and he or she may forget to determine the calibration curve. If the user forgets the determination of the calibration curve, the measurement of blood sugar level cannot be performed appropriately. This is because the determination of the calibration curve should not be entrusted to the user.
Particularly, the correction chip increases the production cost since it requires additional production lines besides the production lines for the biosensor.
The biosensor utilizes various enzymes. In measuring the blood sugar level of the same sample blood, using different enzymes produces different calculation results of the blood sugar level. There are a plurality of standards for measuring the blood sugar level in the world. Each standard provides the kind of enzyme and the required component of blood. For example, the enzyme may be hexokinase or glucose oxidase, while the sample blood may be whole blood or plasma.
Therefore, in countries where the measurement standard provides that hexokinase be used as an enzyme, the blood sugar level measured with glucose oxidase is not appropriate for determining whether or not a patient develops diabetes. Further, when the blood sugar measuring device calculates the blood sugar level with the biosensor utilizing hexokinase, the blood sugar level is not correctly calculated with the biosensor utilizing glucose oxidase.